This invention relates generally to decoking of delayed petroleum coke vessels and more particularly to combination decoking tools having capability for remotely operated cutting mode shifting.
In a delayed coker operation of a petroleum refinery, heavy hydrocarbon (oil) is heated to 900xc2x0 F.-1000xc2x0 F. in large fired heaters and transferred to cylindrical vessels known as coke drums which are as large as 30 feet in diameter and 140 feet in height. The heated oil releases its hydrocarbon vapors for processing into useful products, leaving behind solid petroleum coke which must be removed from the vessel in the decoking cycle of the coker operation in order to prepare the coke drum for further hydrocarbon processing.
Decoking is accomplished using high pressure water jets in two phases. First, a pilot hole, 3 feet to 4 feet in diameter, is cut, or drilled, downward from the top of the vessel through the coke bed using downward oriented nozzles of the decoking tool. Then, the decoking tool is raised to the top of the vessel where either the whole tool or the cutting mode of a combination decoking tool is changed to use sideward oriented nozzles, and the tool, rotated and moved vertically downward in the pilot hole, cuts the balance of the coke and flushes it out the open bottom of the vessel. Removal of the tool from the vessel to either change it out or to change its cutting mode, is a cumbersome and time consuming operation which, considering the cost and limited number of coke vessels, can significantly impact the production capacity of a refinery. Thus, there has been a continuing interest in combination decoking tools which are capable of remotely activated cutting mode shifting. So far, all attempts at providing such tools have failed because of mechanical jamming of mode shifting mechanisms caused by suspended coke debris in the cutting fluid. The debris is the result of recycling of the cutting fluid. Since all previous designs included some form of shuttle valve driven by through-flowing cutting fluid, all were subject to jamming due to debris carried in the cutting fluid which settled or was filtered out of the fluid and gathered between sliding surfaces of valve members. Thus, the very fluid needed to operate the shifting mechanism was the ultimate cause of the failure of the mechanism. In addition, these designs accomplished cutting mode shifting by application of full cutting fluid pressure, thereby increasing friction forces and exacerbating the jamming tendency of the debris laden shuttle devices.
A relatively trouble-free, manually shiftable, combination decoking tool was developed and was described in U.S. Pat. No. 5,816,505, which is commonly owned herewith and is incorporated herein by reference. The trouble-free nature of this tool is attributable to its mode shifting valve design which includes only a rotatable diverter plate for selectively directing cutting fluid to either pilot hole drilling nozzles or full-width coke cutting nozzles. This eliminated most of the moving parts of other shifting mechanisms and; because of the simple rotatable flat diverter plate acting on the flat diverter valve body, it also eliminated the multiple interfaces between parts which provided the jamming sites which caused the failures of earlier designs of remotely operated shifting devices. In spite of these improvements, the tool still needed to be removed from the coke drum in order to change the cutting mode. Thus, there is still no commercially successful decoking tool with a remotely operable cutting mode shifting mechanism.
The foregoing illustrates limitations known to exist in currently available decoking tools. Thus, it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
In one aspect of the present invention, this is accomplished by providing a remotely operated cutting mode shifting apparatus for use with a decoking tool of the type in which the cutting mode is changed by rotation of a diverter valve plate, the apparatus comprising a shifter body adapted for mounting to said decoking tool and having a control rod for engaging with the diverter valve plate; and means within the shifter body for rotating the control rod to drive the diverter valve plate to shift the cutting mode of the decoking tool upon release of cutting fluid pressure from the tool.